'\" et
.TH GETITIMER "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
getitimer,
setitimer
\(em get and set value of interval timer
.SH SYNOPSIS
.LP
.nf
#include <sys/time.h>
.P
int getitimer(int \fIwhich\fP, struct itimerval *\fIvalue\fP);
int setitimer(int \fIwhich\fP, const struct itimerval *restrict \fIvalue\fP,
    struct itimerval *restrict \fIovalue\fP);
.fi
.SH DESCRIPTION
The
\fIgetitimer\fR()
function shall store the current value of the timer specified by
.IR which
into the structure pointed to by
.IR value .
The
\fIsetitimer\fR()
function shall set the timer specified by
.IR which
to the value specified in the structure pointed to by
.IR value ,
and if
.IR ovalue
is not a null pointer, store the previous value of the timer in the
structure pointed to by
.IR ovalue .
.P
A timer value is defined by the
.BR itimerval
structure, specified in
.IR <sys/time.h> .
If
.IR it_value
is non-zero, it shall indicate the time to the next timer expiration.
If
.IR it_interval
is non-zero, it shall specify a value to be used in reloading
.IR it_value
when the timer expires. Setting
.IR it_value
to 0 shall disable a timer, regardless of the value of
.IR it_interval .
Setting
.IR it_interval
to 0 shall disable a timer after its next expiration (assuming
.IR it_value
is non-zero).
.P
Implementations may place limitations on the granularity of timer
values. For each interval timer, if the requested timer value requires
a finer granularity than the implementation supports, the actual timer
value shall be rounded up to the next supported value.
.P
An XSI-conforming implementation provides each process with at least
three interval timers, which are indicated by the
.IR which
argument:
.IP ITIMER_PROF 14
Decrements both in process virtual time and when the system is running
on behalf of the process. It is designed to be used by interpreters in
statistically profiling the execution of interpreted programs. Each
time the ITIMER_PROF timer expires, the SIGPROF signal is delivered.
.IP ITIMER_REAL 14
Decrements in real time. A SIGALRM signal is delivered when this timer
expires.
.IP ITIMER_VIRTUAL 14
Decrements in process virtual time. It runs only when the process is
executing. A SIGVTALRM signal is delivered when it expires.
.P
The interaction between
\fIsetitimer\fR()
and
\fIalarm\fR()
or
\fIsleep\fR()
is unspecified.
.SH "RETURN VALUE"
Upon successful completion,
\fIgetitimer\fR()
or
\fIsetitimer\fR()
shall return 0; otherwise, \-1 shall be returned and
.IR errno
set to indicate the error.
.SH ERRORS
The
\fIsetitimer\fR()
function shall fail if:
.TP
.BR EINVAL
The
.IR value
argument is not in canonical form. (In canonical form, the number of
microseconds is a non-negative integer less than 1\|000\|000 and the
number of seconds is a non-negative integer.)
.P
The
\fIgetitimer\fR()
and
\fIsetitimer\fR()
functions may fail if:
.TP
.BR EINVAL
The
.IR which
argument is not recognized.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
Applications should use the
\fItimer_gettime\fR()
and
\fItimer_settime\fR()
functions instead of the obsolescent
\fIgetitimer\fR()
and
\fIsetitimer\fR()
functions, respectively.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
The
\fIgetitimer\fR()
and
\fIsetitimer\fR()
functions may be removed in a future version.
.SH "SEE ALSO"
.IR "\fIalarm\fR\^(\|)",
.IR "\fIexec\fR\^",
.IR "\fIsleep\fR\^(\|)",
.IR "\fItimer_getoverrun\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<signal.h>\fP",
.IR "\fB<sys_time.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
